The invention pertains to the non-destructive testing of semiconductor material parameters, and most especially to flaw testing of semiconductors by measuring local carrier concentration and gap energy.
In the manufacture of semiconductor devices, such as field effect transistors, one typically begins with a large substrate wafer of semiconductor material, and forms a large number of semiconductor devices in the wafer, finally cutting the wafer into individual devices and packaging them. These manufacturing steps are time consuming and expensive. It is thus of fundamental importance to the manufacturing process of such semiconductor devices that the original wafer of semiconductor material be essentially free of fatal material flaws. Such flaws generally manifest themselves by significant local deviation from desired carrier concentration. Present techniques to test carrier concentration are generally destructive, that is, consume the material tested, rendering it unfit for further use. For this reason, present engineering practice is to sacrifice a very small portion of large semiconductor substrate wafers in the hopes that the small area tested shares the same characteristics of the areas untested, often a very bad and costly assumption. These problems are especially important to the fabrication of gallium arsenide and gallium aluminum arsenide, whose technology is less mature than, for example, that of silicon, and in which one would expect a greater likelihood of undetected fabrication flaws. Thus the semiconductor industry has a plain need for a quick, simple, and inexpensive non-destructive method for measuring local carrier concentration in semiconductors, most especially gallium arsenide or gallium aluminum arsenide.
Additionally, the gap energy of a semiconductor is an important material parameter, the measuring of which is important both in industry and in research. Any technique for quickly, easily, and non-destructively measuring gap energy would be a welcome addition to the art.